Primary Aim 1. Determine frequency of positive SLN by GEP subclassPrimary Aim 2: Confirm whether gene expression profiling (GEP) with the 31-GEP signature (DecisionDxMelanoma) can predict risk of SLN metastasis in patients who are ≥55 years old and have tumors with T1-T2 Breslow thicknessPrimary Aim 3: Combine these results with those of a previously evaluated cohort to improve confidence intervals of SLN metastasis risk prediction